This invention relates generally to the field of signal communication and more particularly, to communication systems using optical signals for transmitting optical-based information and for data communication. Most particularly, this invention relates to signal selection devices useful in the switching or routing of individual optical signal components of DWDM (Dense Wave Division Multiplexed) optical signals.
Optical signals are now used extensively in signal communication systems to carry digital information. Through the use of DWDM, vast amounts of information can be densely packed onto optical signals, which makes the use of such signals highly desirable. DWDM provides a large number of individual wavelengths (at present, about 40 to 60 over each of the C and L bands) which can be simultaneously used to carry data in a single fibre as multiplexed signal components.
Currently, optical signal networks take the form of large rings or hubs, which are cross-connected to smaller local rings, which may in turn be connected to even smaller rings within a very localized area based on a SONET format. Each ring may be operated with specific protocols or framing patterns, data bit rates, compression, synchronisation and the like. At each connection between the various rings, the appropriate optical signals must be connected and directed or routed in the appropriate direction. These connections are currently made by optical-electrical-optical (OEO) switches, which require that the optical signal be converted to an electrical signal, routed, reconverted to an optical signal and then sent on its way. This is an expensive process, especially when there are many DWDM channels and represents a significant bottleneck in the connection and switching operation of optical signal based systems. With the increasing use of mesh network architectures, multiple node networks will require data to travel through multiple switches. In such cases, the use of OEO switches would constitute an even more significant bottleneck.
The use of DWDM allows a single fibre to carry multiple wavelengths which may also be referred as signal components. Typically, fibres will be bundled together to form large capacity information carrying systems. Multiple fibres and multiple signal components per fibre increase the need of routing capacity in the cross-connect. Inherent in such large capacity intersections is a need for enhanced routing capacity, which in turn, drives a need for quick and reliable signal selection for switching or routing purposes.
What is needed is a device that can dynamically and transparently route optical based information- or data-carrying signals according to the intended destination of the information, without the need to convert the signals into electrical signals. Switching signals to different destinations requires separating the signal components from the DWDM signals, selecting the appropriate signal components and switching the same. This may be referred to as dynamic switching which means establishing end to end optical signal paths without the need to manually reconfigure connections. Transparent switching means that the end to end path is established without the need to use OEO conversions.
Recent advances in this field are directed to devices such as, for example, MEMS switches and bubble reflecting arrays that permit the routing of signal components in an optical state. In both of these recent technologies the optical signal is first de-multiplexed into individual signal components. Then the individual signal components are transmitted along a waveguide before being launched into free space at a moveable reflector, either a mirror or a reflective bubble. The reflector can thus be moved to direct the signal component in one or another directions allowing the signal component to be directed to either a first or a second destination, thus permitting routing. However, this method of signal selection and subsequent direction is inherently slow because of the need to physically move the reflecting surfaces between the two positions. Typically the movement of the reflecting surfaces takes place in the order of many milliseconds.
The physical movement of a reflector, while permitting all optical routing, has a number of inherent problems, such as stiction and fatigue or wear of the moving elements over time. Such wear will also limit the number of switching cycles the device can reliably perform. Further, the redirection by means of moveable reflectors limits the geometry of the signal switching. Creating a divergence in the signal path restricts the architecture to a defined input signal plane and a defined output signal plane. Also, the signal component connection requirements must be known before the reflecting array is custom built and the whole device must be removed and replaced if more capacity is needed. Lastly, as the number of signal components being redirected increases, the number of reflecting surfaces required also increases and the overall size of the devices increases. With a larger sized device alignment problems become magnified. One limitation is the use of fibre waveguides to direct each signal component into the reflective array. To even connect the required number of fibres (one for each de-multiplexed signal component) requires a physically large device. What is desired is a means for selecting signal components that does not rely on the physical manipulation of an object such as a reflecting surface and which permits dynamic and transparent optical routing or switching of signal components.
Therefore, what is desired is a reliable selector for selecting signal components from multiplexed optical signals. The selector should operate transparently so the optical signals entering the selector need not be converted to an electrical signal. In this way, any bottlenecks created by OEO switching techniques can be avoided. Further, the selector should be able to respond quickly (i.e. preferably at least as fast as specific SONET restoration times and ideally even faster) and yet be relatively inexpensive to make. Any such selector should also be robust, and be able to reliably operate over time and after many selecting events. Most preferably the device should be capable of having wavelength selection capacity added without creating significant alignment problems. As well the device should be capable of working on signals passing through the device in either direction so as to not be restricted to defined input and output planes to improve flexibility and to reduce costs.
According to a first aspect of the present invention, there is provided a selector assembly to select and deselect signal components from optical signals, said selector assembly comprising:
an input optical connector for optically connecting an input optical signal carrier to said selector assembly;
an output optical connector for optically connecting said selector assembly to an output optical signal carrier;
a signal demultiplexer operatively positioned relative to said input optical connector so that optical signals passing into said selector assembly are demultiplexed by said demultiplexer into signal components, each signal component having a respective signal component beam path;
a signal selector located in each of said signal component beam paths, each of said signal selectors being switchable by the application of an electric field between at least a selecting state and a deselecting state such that each of said signal components may be either selected or deselected;
a controller coupled to said selector element for creating the electric field for switching said selectors; and
a signal multiplexer operatively positioned between said signal selector and said output optical connector for multiplexing said selected signal components together after selection.
According to a second aspect of the present invention, there is provided a method of selecting signal components from optical signals, said method comprising the steps of:
(a) introducing a DWDM optical signal into a selector assembly;
(b) demultiplexing said optical signal into a plurality of signal components;
(c) directing each signal component along a signal component beam path incident to a electro optic selector element;
(d) electronically controlling said electroptic selector element to either select or deselect signal components, and
(e) multiplexing said selected signal components together.
According to another aspect of the present invention, there is provided a signal selector assembly for selecting and deselecting optical signal components from optical signals, said signal selector assembly comprising:
a pair of signal demultiplexer/multiplexers, one located on either side of said signal selector assembly for demultiplexing signals passing into the signal selector assembly and for multiplexing selected signals passing out of the signal selector assembly; and
a signal component selector located between the signal demultiplexer/multiplexers, said signal component selector permitting each optical signal component to pass through in an east only direction, in a west direction only, in both east and west directions simultaneously or in neither direction,
wherein said signal selector assembly provides bi-directional signal component selection.